The diameter of this print is exactly the one of Oreos, the only difference from a normal one is that the filling is higher, so it will look more similar to a “Mega Stuf” version. Realistically if the filling was one of a normal oreo, it wouldn't fit much inside :) so this will fit some pills and small items. 
The container inside is about 8mm high x 35mm in diameter.

Print instructions

Print 2x cookies in one color (generally a dark one like black) and each filling in another color (generally a light one like white) but you can go crazy on the colors :D 
You can glue the fillings with superglue or anything that works with PLA.